Hollow glass microspheres as partial cement replacement for carbon storage well cementation

MARTÍN, CHRISTIAN MARCELO; JEAN MICHEL PEREIRA; DIEGO MANZANAL; GHABEZLOO, SIAVASH; TERESA M. PIQUE

Trondheim

Conferencia; Trondheim Conference on CO2 Capture, Transport and Storage; 2023

SINTEF

Carbon storage is a necessary and well-known climate change mitigation activity that isconstantly being further researched and deployed. There already exists storage sites, whichevidence the importance of studying the different parts involved in it. In this regard, specialattention should be paid to the integrity of the reservoir, the caprock, the casing, and the cementsheath.The cement sheath is generated by injecting the cement slurry until it occupies the annular spacebetween the casing and the formation. During this procedure, some pressure is exerted on theformation, which is proportional to the specific weight of the cement since it is behaving as afluid. On one hand, if this pressure results lower than the pore pressure, the cementation could beincomplete or defective. On the other hand, if the slurry’s pressure results higher than theformation’s strength, it might generate fractures in the formation which would lead to somematerial loss through them. This phenomenon is called circulation loss, and it could result in anexcessive cost increase for the well bore cementation process and also in a defective cementation.Among all the existing alternatives to lighten the cement slurry to avoid circulation loss, partialcement replacement with a lightweight material is the most promising one. In this matter, hollowglass microspheres (HGMS) stand out. These consist of spheres hollow on the inside, of around50 mm in diameter, and mainly composed of borosilicate glass. HGMS can be classified by theirstrength, which ranges from a few MPa to more than 150 MPa. Additionally, this material wasalready proven in previous research to be mechanically and chemically compatible with cementpastes used for cementing well bores.Since carbon dioxide is injected to depths of 850 meters or more, the cement sheath should beable to withstand the associated stresses. A partial replacement of cement by HGMS of differentstrengths alters the mechanical behaviour of the cement sheath and the new compound material was tested to assure that it will be able to resist these conditions. In this research two classes ofHGMS were used, one with a strength of 27 MPa and the other of 41 MPa, in cement pastesCS27 and CS41, respectively. Additionally to these two pastes, a traditional cement paste (CS00)consisting only of cement and water was considered.The mechanical behaviour of these three pastes was determined, which included determining theunconfined compressive strength, the confined compressive strength, their elastic parameters inunconfined and confined conditions, and the elastic parameters obtained in terms of ultrasonicwaves tests. Some changes were appreciated when adding different classes of HGMS whencomparing the results of the three cement pastes proposed. The mechanical and geometricalproperties of HGMS affect the performance of the cement pastes. Furthermore, the changesinduced in the microstructure, as obtained from mercury intrusion porosimetry (MIP) andscanning electron microscopy (SEM), appear to have a correlation with the changes observed inthe mechanical behaviour.Besides, when exposed to carbon storage conditions, traditional Portland cement is known toundergo certain changes in its chemical composition. The phenomenon in which these chemicalchanges are involved is called cement carbonation. It involves the reaction of some of thehardened cement paste components with carbonic acid coming from the dissolution of carbondioxide in water. The carbonation is related to the formation of calcium carbonates (CaCO3)consumption of calcium hydroxide (CH) and calcium silicate hydrates (CSH), both of which arethe main components that grant the strength and the impermeability of the cement.Therefore, it resulted of importance to measure the mechanical behaviour of traditional andlightened cement pastes after cement carbonation. This carbonation was performed in laboratoryconditions, where 20 MPa and 90ºC were reached in a cell containing the cement samples in aCO2 saturated atmosphere with the presence of water. To begin with, HGMS affected thecarbonation effect on the cement samples which already implies some differences in themicrostructure that could be appreciated by MIP and SEM. In addition, the mechanical behaviourwas obtained as aforementioned for all the cement samples proposed in this research after thecarbonation. Some changes in the behaviour could be seen, related to the changes inmicrostructure associated to the advancement of the carbonation in the three proposed cementpastes.All these laboratory results were used to model the behaviour of both, traditional and lightweightcement pastes under true carbon injection well conditions. For this purpose, a finite elementmethod model developed at the École des Ponts ParisTech was used. This model considers thecoupled chemo-poro-mechanical problem for traditional cement pastes, in which an inert phase,CH, CSH and CaCO3 are considered, and the resulting compound material is homogenized. Forincluding the HGMS into the model, it is necessary to update the homogenization equations withthose obtained in some previous research. Once the HGMS were included, the results obtained inthe laboratory were used to calibrate the model and the behaviour of lightweight cement pastesunder actual carbon storage conditions could be modelled.